The present invention relates to a well drilling apparatus designed to be suspended from a travelling block in a drawworks and laterally supported by a dolly running together with the well drilling apparatus along tracks or rails attached to a derrick, which well drilling apparatus comprises at least one driving motor, one power transmission powered by the at least one driving motor, a drive shaft driven from the power transmission and designed to be connected to a drill string, load transferring means, and a torque arresting device attached to and depending from the power transmission.
Well drilling machines that are able to move up and down in a derrick on board a vessel were seriously taken in use in the second half of the nineteen eighties. Till then it had been usual with a rotary table on the drill floor in order to rotate a drill string. The main function of such a drilling machine is to perform the very drilling operation. By this is meant to rotate the drill sting by a given rotational speed and a given torque in order to drill an oil and gas well. The drill string is assembled by a number of pipe elements and can have a length from 300 to 15000 meters.
As the well bore has reached continuously greater depths, the loads and strains within the drilling machines have increased in concert with this. Some kind of development has taken place through the years, but the main concept is in large extent the same as the original one.
Now a totally new generation top drive drilling machine is provided that will ensure stable and continuous operation in far greater extent than before, also during drilling of the continuously deeper wells. In addition to be more sturdy, the new drilling machine will also have the advantage that necessary maintenance work can be performed in a much shorter time than what has been the case with prior art drilling machines.
Examples of the prior art machines are shown and described in NO 155553 and NO 840285.
In such prior art designs the main structural elements consist of an encapsulation of the main thrust bearing, a main shaft having a bolted on load carrying shoulder, and a reduction gear transmission. This means that the load path, i.e. the interconnection between the drilling machine and the drawworks, takes place through the main thrust bearing and the transmission. A breakdown in any of these complicated mechanical components entails complete disassembly of the machine. Normally the most complicated mechanical element is used as main load carrying component. This takes a long time to maintain and represents downtime for the drilling operations of the rig.
This is attempted clarified in table 1, that shows the mutual interconnection of the main components of the prior art solution, i.e. which components that has interface to each other.